1. Field of the Invention
This invention relates to polyurethane elastomers and to their preparation and is more particularly concerned with polyurethane elastomers derived from modified bis(phenyl isocyanate) and with processes for their preparation.
2. Description of the Prior Art
A wide range of thermoplastic non-cellular polyurethanes is currently available for use in the preparation of articles by injection molding, extrusion and like techniques. These elastomers are generally prepared by the reaction of an organic diisocyanate, a polymeric diol, and a difunctional extender. They require care both in the processes used for their manufacture and in the molding processes to which they are subjected in producing fabricated articles. Thus, the materials in question are subject to degradation upon exposure to high temperature for excessive periods during manufacture or processing. In addition, they are extremely sensitive, at the elevated temperatures employed in manufacture and/or processing, to reaction with atmospheric moisture with subsequent undesirable effects on physical properties. The sensitivity to moisture is increased in direct proportion to the temperature to which the polymer is exposed during manufacture and processing. It is accordingly desirable to develop methods for reducing or minimizing these problems.
It is an object of this invention to provide polyurethane elastomers which can be processed, by molding, extrusion and the like, at temperatures lower than those hitherto employed thereby reducing sensitivity to degration by heat and by atmospheric moisture.
It is a further object to reduce the melt temperature of said polyurethane elastomers without significantly affecting the desirable physical properties of said elastomers.
It is a further object to reduce the energy requirements for carrying out the preparation of the said polyurethane elastomers.
These objectives are achieved by adding a trace of a monohydric aliphatic alcohol to the reaction mixture employed in the preparation of said elastomers by a one-shot process.
The use of such monohydric alcohols, commonly referred to in the art as chain terminators, for other purposes is well-known. For example, such monohydric alcohols have been employed (U.S. Pat. No. 3,350,361) in the preparation of isocyanate-terminated prepolymers to be used in coating of leather to give increased break and scuff resistance to the latter. Monohydric alcohols have also been employed in the making of isocyanate-terminated prepolymers which are then reacted with extenders in the presence of solvent for the preparation of spinnable solutions of polyurethane; see U.S. Pat. No. 3,384,623. Polyurethane elastomers have been prepared by reacting isocyanate-terminated prepolymers with diamine, hydrazide or hydrazine extenders, and monohydric alcohols have been used to terminate the reaction; see U.S. Pat. No. 3,483,167. Moisture curable polyurethane coating compositions containing free isocyanate groups have been obtained by reacting a substantial excess of a diisocyanate, a polyol containing some triol, and a monohydric alcohol in the presence of solvent; see U.S. Pat. No. 3,425,973. Monohydric alcohols have been used to terminate the reaction of a diisocyanate, polycaprolactone diol and alkanediol extender (see U.S. Pat. No. 3,761,439) and also to terminate the reaction, in dimethylformamide, or methylenebis(phenyl isocyanate) and a polymeric diol (see U.S. Pat. No. 3,823,111). U.S. Pat. No. 3,272,098 describes the use of monofunctional alcohol in the control of hardness in a clay filled polyurethane elastomer to be used in paving. U.S. Pat. No. 3,875,086 describes what is said to be an improvement over the latter process in that a high equivalent weight (500-2800) monohydroxy polyether is used in place of the lower molecular weight monohydric alcohols.
To the best of our knowledge it has not previously been suggested that a minute amount of a monohydric aliphatic alcohol be included in the one-shot reaction of a diisocyanate, polymeric diol and difunctional extender to prepare a thermoplastic polyurethane and it has not been suggested that such a device would give the highly useful results which are discussed hereinbelow and would achieve the objectives discussed above.